This application claims the priority of International Application No. PCT/EP01/14327, filed Dec. 6, 2001, and German Patent Document No. 100 61 040.4, filed Dec. 8, 2000, the disclosures of which are both incorporated by reference herein.
The present invention relates to a method for actuating a reversible belt pretensioner.
Seat belts which are nowadays usually installed in motor vehicles have a mechanism for automatically winding the loose belt webbing on to a belt winding-on roller which is arranged on a belt reel. The automatic winding on ensures that the belt which is being worn rests loosely against the body of a vehicle occupant and is rolled up on the belt winding-on roller when the seat belt is not in use. The belt is unwound from the belt winding-on roller counter to a torque which is generated by a retraction spring and is also possible when the belt is being worn, in order to permit the vehicle occupant to make a largely free movement.
Furthermore, there is usually a belt extraction lock which, triggered by an actuation device with belt-webbing sensitive and vehicle-sensitive sensor becomes active when the belt is being unwound quickly from the belt winding-on roller, starting from a predefined acceleration of the belt winding-on roller in the unwinding direction, or starting from a predefined acceleration of the vehicle, and secures the belt winding-on roller in its position at the time so that the belt is prevented from unwinding. The locking mechanism which is provided for this purpose is composed of a locking toothing of the belt reel, and of a locking latch which is pivotably mounted and can be pivoted into the locking toothing of the belt reel by means of the actuation device. The toothings on the belt reel and the locking latch are of self-locking design, causing the extraction of the belt to be locked for as long as tensile loading is applied to the belt. If the belt is relieved of this tensile loading, the locking mechanism is returned to its inactive state. This return can be carried out magnetically, electromotively or mechanically, for example by means of a restoring spring on a pivotably mounted locking latch.
In addition, in many seat belts there is a belt pretensioner which increases the protective effect of the seat belt. The belt pretensioner has a drive with an energy store which can be actuated in order to drive a mechanical device by means of the stored energy. In the case of a pyrotechnic energy store, for example, a chemical substance is made to undergo an exothermic reaction by means of a firing element. In this reaction, a gas stream is generated which drives the mechanical device. The driven device is, or can be, mechanically connected to the belt reel, for example, by means of a clutch. Via this connection, the mechanical device exerts a torque on the belt reel. By virtue of this torque, the belt reel rotates with the belt winding-on roller arranged on it and pretensions the unwound belt webbing.
As well as the usual pyrotechnic belt pretensioners which are used nowadays in motor vehicles, it is also possible to use reversible belt pretensioners in vehicles which can be triggered repeatedly, even in rapid succession. These reversible belt pretensioners can have different drives, for example, such a belt pretensioner can be driven by an electric motor. Other reversible belt pretensioners are driven with compressed air from a pressure accumulator or by means of a stressed spring, it being possible to refill the pressure accumulator during travel mode, and for the spring to be restressed during the travel mode.
Reversible belt pretensioners which are driven in this way permit the seat belt to be pretensioned to a predefinable degree, with a predefinable speed and for a predefinable period of time. The multiple triggering capability of the reversible belt pretensioner permits it to be triggered preventatively. Preventative triggering means that the belt pretensioner is triggered in safety-critical travel situations which are detected, for example, by vehicle-movement dynamic sensors or vehicle-surroundings sensors or which are determined by means of the evaluation of the actuation of the brake pedal, of the steering angle or of a driver observation. In addition to preventative triggering, a reversible belt pretensioner can also be used for haptically warning of the driver in safety-critical situations. When there is preventative triggering of the belt pretensioner or when the belt pretensioner is triggered for warning purposes, it is desirable that after pretensioning has taken place and the normal travel mode has been safeguarded, the belt should rest loosely against the vehicle occupant again. The normal travel mode is safeguarded if the evaluation of the situation by a control unit or a hazard computer does not reveal that there is a safety-critical situation.
After reversible pretensioning of the seat belt by means of a reversible belt pretensioner it is possible that the belt extraction lock has become active owing to a belt-webbing-sensitive sensor or a vehicle-sensitive sensor. Examples of belt-webbing-sensitive sensors are a mechanical centrifugal-force sensor in the belt winding in mechanism, an electromechanical centrifugal-force sensor and an electronic belt extraction sensor which senses the extraction speed of the belt or its acceleration. In particular, a belt-webbing-sensitive sensor can respond if, after belt pretensioning, the pretensioned belt is under tensile loading. This tensile loading of the pretensioned belt is in particular dependent on the degree of the pretensioning which has previously occurred and on the sitting position of the vehicle occupant before the pretensioning. As a result of this tensile loading, the belt is unwound again from the belt winding-on roller after the torque exerted on the belt reel by the belt pretensioner drive decreases. If the unwinding of the belt webbing takes place too quickly, the belt-webbing-sensitive sensor responds and the belt extraction lock becomes active. The belt extraction lock can already become active if the belt-webbing-sensitive sensor responds owing to the winding-on operation during the pretensioning of the belt, or the vehicle-sensitive sensor responds owing to the movement of the vehicle. If the belt extraction lock is active, it is no longer possible to unwind the pretensioned belt and the freedom of movement of the vehicle occupant is greatly restricted. The belt webbing is therefore to be released again if a predefined condition is fulfilled, for example, after a predefined time or if the cause of the triggering of the belt pretensioner no longer applies or if a normal travel mode is ensured. In order to release the belt webbing again, in belt extraction locks which are customary today in motor vehicles, the locking latch is to be released from the locking toothing.
The object of the present invention is to improve the application of a reversible belt pretensioner in a motor vehicle.
In order to release the vehicle occupants from the state in which the belt is pretensioned, the locking mechanism is briefly relieved of the tensile loading which is exerted by the pretensioned belt which lies closely against the vehicle occupant. For this purpose, according to the invention, the belt pretensioner is actuated in such a way that the belt reel rotates at least so far in the belt winding-on direction that the locking mechanism is released and releases the belt webbing for unwinding. The releasing of the locking mechanism takes place by virtue of the fact that the tensile loading on the belt webbing no longer exerts any force on the locking mechanism, and that given undercut toothing there is an additional rotation of the belt reel about the undercut of the teeth. The unwinding of the pretensioned belt webbing takes place in such a way that a belt-webbing-sensitive sensor which is present does not already trigger the belt extraction lock due to the desired unwinding operation. After the opening of the locking mechanism, the vehicle occupant is in the belted-up state, with a seat belt which rests loosely against him or is non-tensioned, without the vehicle occupant himself or the driver having to act and without the protective effect of the seat belt failing to be ensured at any time.
In one advantageous development of the method, the belt pretensioner is actuated in such a way that, when the belt webbing is pretensioned and after the locking device opens, the torque of the belt pretensioner drive is not reduced suddenly but rather slowly. This takes place in such a way that the unwinding operation takes place in such a way that the belt-webbing-sensitive sensor does not respond. The slow reduction in the torque takes place, for example, in that the motor current of an electro-motive belt pretensioner is reduced slowly. As a result, the tensile stress which is present in the pretensioned belt reduces more slowly than is the case when the belt pretensioner drive is switched off quickly. The advantage of this development is that renewed triggering of the belt extraction lock by the unwinding of the belt webbing is prevented.
In one advantageous refinement of the method according to the invention, a variable which is indicative of the opening of the locking device is registered. The variable which is indicative of the opening of the locking device is continuously evaluated during the actuation of the belt pretensioner. The opening of the locking device results in a situation in which the belt pretensioner no longer brings about any pretensioning in order to release the belt. The belt pretensioner is actuated in this refinement of the method in such a way that the belt reel rotates just to such an extent in the winding-on direction that the locking device of the belt reel opens and releases the belt webbing for unwinding, and the vehicle occupant is placed in the state with the belt resting loosely against him. The advantage of this refinement is that the loading on the occupants which is caused by the further rotation of the belt winding-on reel when the belt is already pretensioned is as small as possible.
In one advantageous embodiment, the release of the locking latch from the toothing which is located on the belt reel and which is registered by means of a switch is used as a variable which is indicative of the opening of the locking device. The locking latch actuates a mechanical or electrical switch as a function of its state, or is itself part of a switch. It is possible to embody the locking latch itself as a contact switch, part of the locking latch being composed of an electrically conductive material which closes a circuit in a predefined position of the locking latch. An advantage of this embodiment is that the state of the locking latch can be monitored easily and directly.
Alternatively, the rotation of the belt reel or the rotation of an electromotive belt pretensioner drive can be used as an indicative variable. By means of the signal of an angle-of-rotation sensor, the angle of rotation of the belt reel or the angle of rotation of the electromotive drive is registered and it is possible to ensure that the rotation of the belt reel by the belt pretensioner takes place by an angle which is at least of such a magnitude that the locking latch of the locking mechanism is released from the locking toothing. An advantage of this embodiment is that controlled rotation of the belt reel through a predefined angle of rotation is made possible. In a controlled rotation of the belt reel it is possible to open the locking mechanism in such a way that the vehicle occupant experiences as little loading and as few adverse effects as possible.
In one advantageous development of the method with an electromotively operated belt pretensioner, the state of the locking mechanism is registered by the fact that the value of an electrical operating variable of the electric motor is evaluated. Examples of such an operating variable are the motor current, the voltage applied to the motor or the voltage induced by the motor. If the locking mechanism is effective and the belt pretensioned, the motor current and motor voltage exhibit a different characteristic than when the locking mechanism is released with a loose belt, because, in the first case, the motor must work counter to an existing high torque. The advantage of this development of the method is that no additional sensor such as an angle-of-rotation sensor or a sensor for the position of the locking latch is necessary.
In one advantageous development of the invention with a drive for a seat adjustment means, the latter is actuated in order to open the locking device. A drive for a seat adjustment means can have, for example, an electrical or pneumatic power supply, and the drive is actuated via the control of the power supply or the supplied air pressure. If the belt extraction lock is active after belt pretensioning has occurred, the tensile force in the belt may, depending on the degree of belt pretensioning, be such that further pretensioning of the belt webbing by the belt pretensioner drive does not lead to a rotation with a sufficiently large angle of rotation, and the locking mechanism is not released. By actuating a seat adjustment means, the sitting position can be changed to the extent that the tensile force in the belt is reduced and that the subsequent pretensioning of the belt webbing by the belt pretensioner drive leads to a sufficiently large angle of rotation of the belt reel and to opening of the locking mechanism. In particular, lowering of the sitting area, displacement of the seat to the rear and inclination of the seat backrest to the rear cause the belt webbing to be relieved of tensioning. So that the vehicle occupants are adversely affected as little as possible, there may be provision for the adjustment facilities of the seat to be actuated only if the opening of the locking device according to one of the methods as described in the previous paragraphs was unsuccessful.
As an alternative to the adjustment of the seat, an electrically or pneumatically driven adjustment device of the belt deflection roller, which is provided for adjusting the height of the belt, can also be actuated in such a way that this belt deflection roller is lowered in order to open the locking mechanism. An advantage of this alternative embodiment is that the adverse effects on the vehicle occupants which occur due to actuation of the adjustment device of the belt deflection roller are reduced in comparison with the adverse effects which occur when the seat adjustment device is actuated. The actuation of the adjustment device of the belt deflection roller can also always take place in addition to an actuation, or immediately before an actuation according to the invention of the belt pretensioner drive, with the objective of reducing the loading on the vehicle occupants.
As the setting operations of the seat adjustment means and of the belt deflection roller are normally performed in such a way that in the case of small vehicle occupants the belt deflection roller is located further down and the seat further to the front, and in the case of large vehicle occupants the deflection roller is located further up and the seat further back, the pretensioned and locked belt webbing can always be relieved of loading by a combination of actuation of the belt deflection roller and actuation of the seat adjustment means. An advantage of this development is that even in the case of pretensioning with a high pretensioning force, the locking device can be reliably opened without the drive of the belt pretensioner being configured in such a way that it has a torque reserve which is provided only for opening the locking device, but not for the actual pretensioning operation.
It is also possible to actuate the belt deflection roller and the seat adjustment means either individually or in combination in order to release the locking mechanism, without the belt pretensioner drive being actuated. This has the advantage that it is not necessary to provide a belt pretensioner which permits the locking device to be opened in accordance with the method according to the invention.